1 1. Give an account of the ways in which molecules and ions move into and out of cells. ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ (Allow 2 lined pages) (Total 10 marks) 2. The table below refers to four membrane transport processes: diffusion, facilitated diffusion, osmosis and active transport. If the statement is correct, place a tick ( ) in the appropriate box and if the statement is incorrect, place a cross (X) in the appropriate box. Process Takes place against a concentration gradient Requires energy in the form of ATP Diffusion Facilitated diffusion Osmosis Active transport (Total 4 marks) 3. (a) Explain what is meant by the term diffusion. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (2)
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1. Give an account of the ways in which molecules and ions move into and out of cells.
2. The table below refers to four membrane transport processes: diffusion, facilitated diffusion, osmosis and active transport. If the statement is correct, place a tick ( ) in the appropriate box and if the statement is incorrect, place a cross (X) in the appropriate box.
Process Takes place against a concentration gradient
Requires energy in the form of ATP
Diffusion
Facilitated diffusion
Osmosis
Active transport
(Total 4 marks)
3. (a) Explain what is meant by the term diffusion.
(b) In an investigation into the effects of osmosis on red blood cells, seven samples of red blood cells were placed in potassium chloride solutions of different concentrations. After two hours, each sample was examined to find the percentage of cells that had swollen and burst (lysed). The results are shown in the graph below.
100
90
80
70
60
50
40
30
20
10
00.04 0.05 0.06 0.07 0.08
Concentration of potassium chloride /mol dm
Percentage ofred bloodcells thathad burst
–3
(i) Calculate the difference between the percentage of red blood cells that burst in 0.05 mol dm–1 and 0.07 mol dm–1 potassium chloride solutions. Show your working.
Answer ................................ (2)
4
(ii) With reference to water potential, explain why most of the cells burst when placed in 0.05 mol dm–3 potassium chloride solution.
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……………………………………………….………………………………. (3)
(iii) Suggest what would happen if red blood cells were placed in a 0 1 mol dm–3 solution of potassium chloride.
……………………………………………….……………………………….
……………………………………………….………………………………. (1)
(c) Explain why plant cells do not burst when placed in distilled water.
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……..……………………………………………….……………………………….
……..……………………………………………….……………………………….
……..……………………………………………….………………………………. (2)
(Total 12 marks)’
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5. An experiment was carried out to test the effect of different temperatures on beetroot cell membranes.
Beetroot cells contain a red pigment which is normally held within the cell by the membrane. If the cell membrane is damaged, red pigment will leak out of the cell.
Five identical discs of beetroot tissue were carefully washed in distilled water until no red pigment was seen in the water. These discs were then carefully transferred to a test-tube containing 10 cm3 of distilled water maintained at 25 °C in a water bath and left for 30 minutes. After this time the liquid was carefully poured off and the concentration of red pigment it contained was measured in a colorimeter. The greater the concentration of red pigment the higher the absorbance shown on the colorimeter. This was then repeated using a second batch of similar beetroot discs at the same temperature.
The whole procedure was then repeated at four different temperatures.
A copy of a student’s laboratory notebook showing the results of this investigation is given below.
Absorbance in arbitrary units
25 ºCReading 1 0.13
Reading 2 0.09
37 ºCReading 1 0.17
Reading 2 0.19
47 ºCReading 1 0.54
Reading 2 0.58
56 ºCReading 1 0.93
Reading 2 0.99
65 ºCReading 1 3.42
Reading 2 3.56
(a) Prepare a table and present the results in a suitable way so that the concentration of red pigment leaking from the beetroot cells at different temperatures can be compared.
(4)
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(b) Use the data in your table to present the information in a suitable graphical form (4)
(c) Describe the trends and patterns shown by these data. (2)
(d) Describe two limitations of this method that could give rise to inaccurate results. (2)
(e) What conclusions can be drawn from this investigation? (2)
(Total 14 marks)
6. An experiment was carried out to compare the uptake of two substances, A and B, by Amoeba. Amoeba is a single-celled aquatic organism.
Cells of Amoeba were placed in a solution containing equal concentrations of both substances and kept at 15 °C. The concentration of each substance in the cytoplasm of the cells was measured every 30 minutes over a period of 6 hours.
The results of this experiment are shown in the graph below.
Substance A
Substance B
14
12
10
8
6
4
2
00 1 2 3 4 5 6
Time / hours
Concentrationin cytoplasm/
g cmµ –3
7
(a) Compare the uptake of substance A by the cells with the uptake of substance B during the period of 6 hours.
8. Cylinders of potato were placed in sucrose solutions of different concentrations for 12 hours. The graph below shows the percentage change in length of the cylinders after 12 hours.
Percentagechangein lengthof thecylinders
+10
+8
+6
+4
+2
0
–2
–4
–6
–8
–10
Concentrationof sucrosesolution mol / dm –3
0.1 0.2 0.3 0.4 0.5 0.6
10
(a) Explain the change in length which occurred when a cylinder of potato was placed in a sucrose solution of concentration 0.3 mol dm–3.
(b) During spring, shoots grow out of potatoes. This causes a rise in the concentration of sugars in the potatoes.
(i) Draw a curve on the graph opposite to represent the changes in length you would expect if the investigation had been carried out with potatoes that had grown shoots.
(2)
(ii) Explain why the curve you have drawn has this shape.
(c) The graph below shows the results of an experiment to investigate the effect of temperature on the permeability of beetroot cell membranes. The intensity of the colour in the water surrounding the beetroot was measured at the temperatures indicated on the graph.
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
030 40 50 60 70 80
Temperature / ºC
Intensity ofcolour/ arbitrary units
(i) Outline a procedure that you could have used to produce these results.
(b) The proteins in the cell surface membranes of two cells (A and B) were stained using different coloured dyes. One cell’s membrane proteins were stained with a green dye and the other cell’s membrane proteins with a red dye. The cells were then fused (merged together) to form one cell.
The diagram below shows the distribution of the proteins in the cells before and after fusion.
Use your knowledge of the properties of cell surface membranes to explain these results.
(c) Facilitated diffusion and active transport are two ways in which molecules are transported across cell membranes. Describe one similarity and one difference between facilitated diffusion and active transport.
13. (a) Beetroot cells contain a red water-soluble pigment in their vacuoles. This pigment cannot pass through membranes. If the membrane is damaged, red pigment will leak out of the cell.
An experiment was carried out to test the effect of different temperatures on beetroot cell membranes. Eight equal-sized discs of beetroot were cut and carefully rinsed in distilled water.
One disc was transferred to a test tube containing 10 cm3 of distilled water maintained at a temperature of 25 °C and left for 30 minutes. After this time, the intensity of red coloration of the liquid in the test tube was measured using a colorimeter.
Each of the other seven discs was treated in a similar way but maintained at a different temperature.
The results of the investigation are shown in the graph below.
20 30 40 50 60 70 80 90 100
Intensity ofred coloration/arbitraryunits
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
Temperature / ºC
20
(i) Describe the effect of increasing temperature on the intensity of the red coloration of the solution.
14. For a cell to function normally, it needs to be able to control the transport of molecules and ions across its surface membrane. Complete the following passage by writing the appropriate word(s) in each space.
(a) Molecules and ions move into cells by a variety of methods. Oxygen passes
passively into cells by ............................................... Hydrophilic molecules that
are larger than gases pass into cells with the aid of membrane proteins in another
passive process called ............................................... If substances are being moved
against a concentration gradient, a method called ..............................................
is used. This requires input of .............................................. and involves
.............................................. proteins in the membrane. Bulk transport of materials
into cells is by ............................................... (3)
(b) Give one similarity and one difference between the following methods of transport across cell membranes:
(b) Experiments were carried out to compare the uptake by cells of a substance (substance X) in the presence and absence of a respiratory inhibitor. A respiratory inhibitor is a substance that prevents the formation of ATP.
In each experiment the cells were incubated in a solution of substance X for five hours.
The concentration of substance X in the cytoplasm was measured throughout.
The graph below shows the changes in the concentration of substance X in the cell cytoplasm during the experiments.
14
12
10
8
6
4
2
Con
cent
ratio
n of
subs
tanc
e X
insi
de th
e ce
ll /
g cm
µ–3
0 1 2 3 4 5Time/ hours
Cells incubated withsubstance X only
Cells incubated withsubstance X and therespiratory inhibitor
25
(i) Describe the changes in the concentration of substance X in the cytoplasm of the cells incubated with the respiratory inhibitor present, during the five hours of the experiments.
16. (a) The diagram below shows a model of the cell membrane and various molecules being transported through the membrane into the cell.
Z
R
Y
P Q
X
(i) Name the structures labelled X, Y and Z.
X ........................................
Y ........................................
Z ......................................... (3)
(ii) Name the transport process across the membrane shown by the different molecules and their arrows P, Q and R.
P .........................................
Q ........................................
R ........................................ (3)
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(b) Cystic fibrosis is caused by a mutation in a gene coding for a membrane protein. Explain why people suffering from cystic fibrosis find it difficult to digest their food.
17. Read through the following account of the transport of molecules across a cell surface membrane, then write on the dotted lines the most appropriate word or words to complete the account.
Some molecules cross a cell surface membrane by passing down a
concentration gradient through the phospholipid layer. This process is called
................................................ Some polar molecules cross the membrane by combining
with transport proteins which can change their shape. When this movement occurs
down a concentration gradient, the process is called ...............................................
and when it occurs against a concentration gradient the process is called
................................................ Most movement of molecules against a concentration
gradient uses energy in the form of ................................................ (Total 4 marks)
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18. All cells have a cell surface membrane. It contains many different molecules and its structure has been described as a fluid mosaic.
(c) Cholesterol is an important component of many cell surface membranes.
Diagram A is an annotated diagram of a cholesterol molecule. Using your knowledge of the properties of phospholipids, draw one cholesterol molecule in an appropriate position in the phospholipid bilayer on diagram B.
Phospholipid bilayerNon-charged
region
Charged region
Cholesterol molecule
Diagram A Diagram B
(2)
(d) Cholesterol is also found in the blood. Different types of lipoprotein are involved in transporting cholesterol in blood.
Describe how the different types of lipoproteins can affect the health of the body.
19. The table below refers to four processes by which molecules can cross a cell surface (plasma) membrane. If the statement is correct, place a tick ( ) in the appropriate box and if the statement is incorrect, place a cross ( ) in the appropriate box.
Process Requires carrier proteins Requires energy in the form of ATP
Simple diffusion
Facilitated diffusion
Osmosis
Active transport (Total 4 marks)
20. All cells have a cell surface (plasma) membrane. The diagram below shows the structure of this membrane.
Proteins
Phospholipid bilayer
Explain how the properties of phospholipids result in the formation of a bilayer.
21. Some cells from the small intestine were placed in a solution containing amino acids. The diagram below shows the movement of these amino acids over a 15 minute period.
Amino acids found at ribosomes where they are joined together to form protein
Amino acids found in the cytoplasm of the cells
Amino acids move through the cell surface membrane into the cells
(a) (i) Name two mechanisms by which amino acids can move through the cell surface membrane.
(ii) Assuming that the start codon on mRNA is three bases long and the stop codon is also three bases long, calculate the minimum number of bases in the mRNA needed to code for a protein that is 300 amino acids long.
22. Animals have evolved a heart and a circulation system as a mechanism which overcomes the limitations of diffusion. However, diffusion is still important in animals. For example, calcium (Ca2+) ions can be absorbed by facilitated diffusion from the bloodstream into muscle cells.
(a) Describe how ions such as Ca2+ pass through the cell surface membrane by facilitated diffusion.
23. (a) The table below refers to three transport mechanisms. If the statement is true, put a cross in the appropriate box.
Statement Osmosis Facilitated diffusion
Active transport
Movement of water
Requires ATP
Molecules move down their concentration gradient
Carrier proteins are needed (6)
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(b) An experiment was carried out to measure the uptake of substance B by some red blood cells.
The red blood cells were placed in a solution containing substance B and kept at 25 °C. The concentration of substance B in the cytoplasm of the cells was measured every hour over a period of 10 hours.
The results of this experiment are shown in the graph below.
00
2
42
4
6
86
8
10
12
14
16
18
20
Time / hours
Concentrationin cytoplasm / µg cm-3
10
Substance B
36
(i) Describe the changes in cytoplasm concentration of substance B shown in the graph and explain how these changes support the statement that substance B enters the cells by diffusion.
(b) The graph below shows how the permeability of three different membranes to substance A changes with temperature. One of the membranes contains no cholesterol, one of the membranes has a low cholesterol content and the third membrane has a high cholesterol content.
Temperature / °C
Permeabilityof membraneto substance A / arbitrary units
3020100
(i) Describe the effects of the presence of cholesterol and of an increase in temperature on the permeability of the three membranes to substance A.
